The present invention relates generally to oil seals, and more particularly, to improved oil seals which combine excellent sealing action, a certain oil return pumping or hydrodynamic capability, reduced temperature running, longer wear, and freedom from damage occasioned by use in relatively severe exterior environments.
Oil seals made according to the present invention are an improvement to the type of seal described and claimed in U.S. Pat. No. 3,929,340, issued Dec. 30, 1975.
Seals made according to the above-identified patent provided a marked increase in predictable seal life, and combined reduced temperature running with a pumping or hydrodynamic action characterized by the ability to return to the sealed region small amounts of oil which might otherwise have collected just outside the sealed region and which might, therefore, create a problem of leakage. Seals of this type are also advantageous in that, within normal limits, although providing good pumping action, they do not provide a pumping action which is either too great, or an action which is too small to be ineffective. At the same time, seals of this type lack external projections such as ribs or vanes on the exterior or air side of the seal band, and, accordingly, these improved seals tend naturally to ingest less dirt and dust than do other types of known hydrodynamic seals.
Inasmuch as any hydrodynamic or pumping seal is capable of pumping oil tending to escape between the seal band and the shaft or the like, such seals inherently may also undesirably return a certain amount of dirt or dust to the sealed region.
Accordingly, a very desirable seal would be one which would ingest little, if any, dust or dirt in normal use, but which would still retain the pumping capability and the cool running characteristics associated with a sinuous seal band type primary lip configuration. A seal of this type would be very desirable if effective means were provided for keeping dust and dirt, particularly large quantities thereof, from the vicinity of the primary seal band.
In this connection, seals of the type referred to in U.S. Pat. No. 3,929,340, have been produced both with and without a so-called dirt lip or excluder lip. Seals utilizing lips of this kind normally do so for the purpose of keeping moderate amounts of dust from the primary lip region, however, seals of this kind have not proved entirely capable of excluding physically large or heavy amounts of dirt, mud or the like from the region adjacent the primary seal band.
This is because, among other reasons, the size and shape of the ordinary dust lip associated with such a seal is mall and flexible, and will rapidly wear in use so as to permit a measurable clearance between the shaft or other sealed member.
Even where dust lips have been provided which have been partily or even moderately successful, such lips tend to have the inherent drawback of dry running, that is, operating in the absence of lubricant. This, in turn, causes elevated temperatures in the vicinity of the dust lip and tends to reduce the flexibility or even cause embrittlement.
Accordingly, the addition of an ordinary dust lip of the known type to a seal having a sinuous primary lip, constitutes a certain improvement over sinuous seals without dirt lips; however, dirt lips or seals of this sort have not proved successful in overcoming the problems of severe use, that is, use in sealing shafts in environments such as those environments utilizing farm equipment and the like, wherein the seal itself is exposed to the atmosphere or environment and is not largely protected by surrounding mechanisms such as large flanges, bell housings, vibration dampers, slinger members, or other mechanical parts.
In view of the foregoing limitations of some prior art seals, and in view of the desirable characteristics which should be embodied in an improved sinuous seal for external applications, it is an object of the present invention to provide an improved oil seal for use in severe environments.
Another object is to provide a fluid seal which includes the advantages of sinuous lip prior art seals, and which further includes the advantages of improved dirt exclusion and adaptability to extremely dirty and dusty environments.
Still another object is to provide a fluid seal which includes both elastomeric and relatively rigid means for excluding dirt from the area between the primary sealing lip portion of the seal assembly and the innermost dirt lip.
Yet another object is to provide a seal having a plurality of dirt and dust exclusion lips which are distorted from an unstressed or as-manufactured position into a distorted position of use and in which the primary seal lip is distorted only slightly upon installation.
Another object is to provide a fluid seal which is particularly adapted for reception of a charge of grease or other viscous lubricant in the areas of the dirt lips, and which can therefor be operated under extreme conditions without generating an intentionally high temperature rise in the vicinity of the excluder lips and in the vicinity of the excluder flange of the seal casing.
A still further object is to provide an oil seal assembly which includes both inner and outer elements comprising a composite casing, and in which the outer casing unit protects an elastomeric dirt lip and serves as an excluder for large dirt particles.
The foregoing and other objects and advantages of the invention are achieved in practice by providing an oil seal having a rigid exterior casing and a dirt exclusion assembly comprising a plurality of radially extending excluder lips spaced axially apart from each other and having substantially reduced diameters with relation to a shaft to be sealed, and a primary seal lip assembly which includes first and second, axially indulating, frustoconical lip surfaces meeting each other along an axially undulating line to form a seal band area with an axially sinuous pattern.
The manner in which the foregoing and other objects and advantages are achieved in practice will become more apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, in which the like reference numbers indicate corresponding parts throughout: